Right-handed reliever Darren O’Day is scheduled to throw off a full mound Monday for the first time since going on the disabled list, but Showalter and O’Day said they don't know what the next step will be in his recovery from a right shoulder strain.

“I’m not sure,” Showalter said. “We’re going to see how that goes. Roger [McDowell, pitching coach] and Richie [Bancells, head athletic trainer] will sit down with Darren. He’s been down this road a few times, so we’re going to kind of lean on him, when he’s ready, when he’s not ... .

"But it would be nice to get him and Zach back because we’ve had a lot of situations where we weren’t able to stem the tide so to speak. With one of those guys, we’re able to move [Mychal Givens] and some of those guys around when we’ve got all four of them. I was really hoping someone would seize the opportunity they’ve been given.”

O’Day said he anticipated just a short minor league rehabilitation stint before returning from the DL.

“I hope so,” he said. “I want to get back.”

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On Sunday, catcher Welington Castillo started for the ninth straight day since returning from the disabled list June 10. Castillo was rested late in the past two games, and Showalter wanted to start him in Sunday’s day-after-night game because of his strong numbers against St. Louis Cardinals right-hander Lance Lynn.

Castillo entered the game 6-for-9 against Lynn with a pair of solo homers among those hits.

“We’ve taken him out of the last two games early,” Showalter said. “We talked about it before the series started to see how it went. Cassy wants to catch every game. He doesn’t believe in that day game [after] night game [rest].”

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Closer Zach Britton’s first minor league rehab outing Monday at Short-A Aberdeen could be threatened by bad weather, so if that game is rained out, Britton would just push his outing to Tuesday. He is scheduled to throw the first inning.

“His schedule has kind of built in some rain days,” Showalter said. “But that won’t change much. I know Tuesday looks a lot better. They’re the only team at home.”